Diagnostic Approach to Cardiac Amyloidosis

Initial Evaluation and Diagnostic Criteria

The American College of Cardiology recommends echocardiography as the primary initial diagnostic imaging tool for patients with suspected cardiac amyloidosis 1
Cardiac MRI (CMR) is rated as "Appropriate" for initial screening of cardiac amyloidosis and can detect cardiac involvement with high sensitivity 3, 4
Blood tests to exclude AL amyloidosis, such as serum free light chain assay, serum and urine immunofixation electrophoresis, must be performed before proceeding to 99mTc-PYP/DPD/HMDP scintigraphy 5

99mTc-PYP scintigraphy is specifically indicated for diagnosing ATTR cardiac amyloidosis after excluding AL amyloidosis 7, 2
A positive bone scintigraphy, defined as a Perugini score ≥2 and/or heart-to-contralateral lung ratio >1.5, allows diagnosis of ATTR cardiac amyloidosis when no monoclonal protein is found 1
The American Heart Association suggests that 99mTc-PYP scintigraphy is rated as "Rarely Appropriate" for patients with suspected AL cardiac amyloidosis 3, 4

Visual grading (Perugini score) ≥2 on a 99mTc-PYP scan after 1 or 3 hours is considered positive 1
Heart-to-contralateral lung (H/CL) ratio >1.5 on a 1-hour scan or >1.3 on a 3-hour scan is considered positive 1, 2
SPECT imaging is recommended in addition to planar imaging to differentiate myocardial from blood pool signal 2, 8

A critical pitfall is that a positive 99mTc-PYP scan in the context of any abnormal monoclonal protein evaluation should NOT be considered diagnostic for ATTR cardiac amyloidosis and requires further evaluation 3
Excess blood pool activity on 1-hour images may lead to false positive interpretations 9
Over 10% of patients with monoclonal gammopathy can have ATTR deposits, making tissue typing essential in cases with both positive 99mTc-PYP and abnormal monoclonal protein studies 5